The Specific Electrode Potential of Bismuth Citation Sticht, Robert Carl, Jr. (1918) The Specific Electrode Potential of Bismuth. Bachelor's thesis, California Institute of Technology. doi:10.7907/2wr9-sr76. https://resolver.caltech.edu/CaltechTHESIS:07192024-214358601 Abstract No abstract. Item Type: Thesis (Bachelor's thesis) Subject Keywords: (Chemical Engineering) Degree Grantor: California Institute of Technology Division: Chemistry and Chemical Engineering Major Option: Chemical Engineering Thesis Availability: Public (worldwide access) Research Advisor(s): Unknown, Unknown Thesis Committee: Unknown, Unknown Defense Date: 1 January 1918 Record Number: CaltechTHESIS:07192024-214358601 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:07192024-214358601 DOI: 10.7907/2wr9-sr76 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 16577 Collection: CaltechTHESIS Deposited By: Benjamin Perez Deposited On: 23 Jul 2024 16:56 Last Modified: 23 Jul 2024 17:08 Thesis Files PDF - Final Version See Usage Policy. 6MB Repository Staff Only: item control page

The Specific Electrode Potenti al of Bismuth War Class of 191$ . Robert C. Sticht, Jr. Throop College of Technology. The specific Electrode Potential of Bismuth, Bismuth is one of the most important metals the specific electrode potential of which is not accurately known. The experir:1enta J. determination of this is rende:red difficult by the :fact that in the case of bismuth the simple salts, such as the chloride, nitrate,and sulfate, v1hich are usu.ally employed in su.ch. d.eterminattons, are strong ly hydrolysed in solution forming insoluble basic compounds. Previous work. 1 Neuman determined the :potential of ·bismuth againsl solutions of the chloride, nitrate,and su.12 fate . Owing to the uncertainty of the concentration of the 'bismuth-ion in these solutions, he made no attem~t to calculat8 the specific electrode potential. 1. Bernhard Neuman, zeit. Phys. Chem. 14,P.193,1894 2. Obtained by adding the chloride, nitrate and sulfate to water in the proper amounts to make one molal solutions, and :filtering off the precipated basic salt. Page 1 Foerster and schwabe1 measured the potential of bismuth against a o.65 normal solution of bismuth :fluosilicate, B12 (SIF6 )3 • The value f'ound,referred to the hydrogen electrode,was -0.295 velt#. Again, because of uncertainty in the ion concentration in this solution,the specific electrode potential was not calculated. .2 The value given in most elementary text books 3 is-0.39 volt•. ~ 4 This value is used by Palmer , fn his discussion of "Electrolytic Potentials and the P eriod.io system". In all these re:ferences the value given is followed tw a question mark. Abegg, Auerbach, 5 and Luther, in their recent compilation of' electromotive force data and in a later sUJ)plement_,give the value -0.2 volt*• 1. F.Foerster and E.Schwabe, zeit fur Electroch.em. 16, P.280, 1910. • 2. Alexander smith, Inorganic Chemistry (1910) W.A.:uoyes, Textbook. o:f Chemistry (1913). 3. All electrode potentials in this paper are referred. to the Molal HYd@gen electrode. The electrode potential is considered positive when positive electricity tends to f'low :from the electrode to the solution. 4. Nernst•s Festschrif't, 336 (1912). 5. Messungen elektromotorischen Kraf'te galvanischer Kette~ mit waaserigel'¼e Elektrolyten, R.Abegg, Fr. Auerbach and R. Luther. ( 1911) Page 2 This discrepancy seems to be due to the fact that the value given in ~he text books was apparently taken 1 from a compilation by Wilmnore, who recalculated the data of various investigators. He gives the speci:fic electrode potential of bismuth as less than -0.391, basing his calculations on data of Neuman. Unfortunately, Wilsmore gave the wrong sign to the bismuth cells measured by Neuman. Neuman found the electromotive force of the cell: Bi, B1Cl3 ( saturated sol.) ,Indifferent electrolyte, KCl (1.0M. ), Hgz Clg'f- Hg. to be o.145 volt,4'. Taking the ttabsolute" potential of the normal calomel electrode to be -0.560 he made the following addition: Bi ,BiC13 / / Normal ce.lomel ..... ;- .145 Normal CalOIIlel // Absolute zero -.56 B1, BiCl3/ / Absolute zero -.1:15 volts Taking this same data Wilmore calculated as follows: B1,B1Cl // Normal Calomel -.145 Normal Calomel // Molal Hydrogen -.283 Bi,BiCl // Molal Hydrogen -.428 volts. 1. n.T.M.. Wilsmore, Zeit. PhYs. Chem. 35, 316, 1900. Page 3 This 1s the value :from which he calculated the specific electrode potential of bismuth to be lees ~1 than -0.30. The chief difficulty in determining the value of the specific electrode potential of bismuth is due, as has been pointed out, to the uncertainty of the i~on concentration in the solutions of bismuth salt. The common salts of the tri-univalent tYI>e, such as t.h.e chloride, nitrate, etc., which are commonly employed in determinations of this kind, give insoluble hydrolysis pro4ucts, wh.ile the degree of ionization of the more complex salts is ~ery uncertain. The perchlorate, ~owever, offers pecu- liar advantages for this determination,sir:ice it does not give insoluble hydrolysis products atmoderate conceJD.trations. l. That Wilsmore used the same sign convention as Ne1tman is evident from the following: Neuman measured the potential of the cell Ag, AgN().3(1MJ, Indifferent electrolyde (lM~, K Cl ( lM. rH~ ClBt Hg. and found it to be -0.495 volts. He then made the following id,dition: Ag, AgNO / Nor7'1 calomel -.495 volts Normal ca~o;nel "Absolute" zero -,560 Ag, AgNO fl "Absolute" zero -1.055 volts Page 4 The present detenuination waa carried out by measuring the electromotive force of a bismuth electrode 7 in a solution of bismuth perchlorate and percl1loric aoid1 against a hydrogen electrode~ in a solu-:t ion of perchloric acid of approximately the same concentration. 'l'O check the above determination the equili- brium of the bismuth-ion, .. ou.pric-inn,: . metallic bismuth and metallic copper was investigated. Preparation of the Chemicalsr The perchloric acid was obtained f'rom the Genessee Chemical works. It gave no test for chlorides, sulfates or iron, and left no residue when evaporated to dryness. sent ~ 1n small amomits. Chlorates were pre- The strength of the ~oluwii-h tions was determined by titrating~ standard sod• itrm hydroxide. (uote continued) using this· data Wilsmore calculated as follows: Ag? AgN03 // Morrr,.al Calomel -. ·495 Normal Cal9mel // Molal Hydrogen;,,283 At~"AgNo 3 / / Molal Hydrogen - • 778 vol ts. From this Wilsrnore calculated the value of the specific electrode potential to be less than -. 780 volts. This agrees with recently determined values. Page 5 The bismuth was made by electrolytic precipitation :from a strong solution of bismuth chloride in six .norrnal hydrochloric acid, between platinum anodes and cathodes ,.and using a high current density. The metal was precipitated. as a loose, spongy mass, which fell off the electrodes at intervals and sank to the bottom of the vessel. The metal was ground in a mortar with dilute nitric acid, and then washed soni~ fin,e. a'fnr with vvater. The washing was repeeted. until" the wash- water no longer sh.owed traces of chlorides. The metallic bismuth was converted into the oxide by heating in an open porcelain dish. The ·b ismuth perchlorate was obtained by heating the bismuth oxide with perchloric acid. 1he first solutions were made by dissolving the metal in perchloric acid, but it was found that it was necessary to evaporate the acid until it was very concentrated, in order to dissolve the metal at all rapidly. At such concentrations the acid is unstable and on several occasions it exploded violently. The solubility of bismuth perchlorate in one-tenth norrrial perohloric acid was less than 0.02 normal. Since solutiohs weaker than 0irOOl normal could not be ra9-ge of analyzed accurately, the/concentrations over which measurements could be made was very limited. Page 6 1 Hydrogen was made by the electrolysis of an alkaline solution of sodium sulfate. The gas was passed through potassium pyrogallate, acid diohromate ,c: and finally through perchlor~ acid of the same strength as that used. in the cell. This last was in a saturator attached to the cell and rocked with it in the thermostat. ne·s cription of Apparatus , The bismuth cetl {Figure 1) (a) consisted of two compartments connected together at the bottom. Each compartment was provided with two hollow ground glass stoppers ( d). r~. were sealed to C be submerged in To th.e upper port ion of these, tubes F!!J. l- I I 'D / allow the cell to the thermostat • .ti To the lower end of one of the d- stoppers in each compartment, a tube was sealed extending to the level of the liqiud. Into the lower end of' this tu.be was sealed a platinum spiral. Page 7 The bismuth electrodes were made by depositing bismuth on the platinum spirals. It was found that the most coherent coats were obtained by plating from a weakly acid solution ( about o. 05 normal), using a current density of not more than 0.005 amperes per 0 square centimeter and a tem:peratu.re of about 60 c. Electrodes thus prepared. f'rom the bismuth o~bhloride, made in the purification of the bismuth chloride desc~;f bed ,above, agreed with those made from bismuth p erchlorate and Kahlbaum•s bismuth nitrate within 0.0005 volts, which was as closely as electrodes prepared from the same solution agreed with each other. Since adherent coats could be more easily contained from the nitrate and the perchlorate than from the chloride, all electrodes used. in the final measurements were 1r:ade from solutions of the,se salts. The open stoppers in the two oolilJ;)artmente allowed air to be drawn in and expelled when the cell was rocked, thus enabling the liquid to surge from one chamber to the other. The rise and fall was about one-half to three-quarters of an inch,a.nd the rate of rocking was 40 cycles per minute. In this way ample stirring of the solution was obtained. Page 8 The hydrogen cell (b) had but one compartment. The hydrogen electrodes were made by platinizing platinum foil. No lead acetate was used in this operation as it appears to be unnecessary and may be a source of error. After a good coating had been deposited, sulphuric acid was poured into the cell and the current commutated at five minute intervals for about 40 minutes, then at minute intervals for-· 20 minutes. After one or two preliminal'lt runs had been made the difference in potential between the electrodes thus prepared was less than 0.00001 volts. Hydrogen was bubbled over the electrodes from a capillary tube (f) which extended almost to the bottom of th.e cell. It then escaped through the outlet tube (g). The hydrogen cell was connected to the bismuth cell by the siphon tube (c). At the top of this was a three-way stop-cock (c) to whose third arm a second stop-cock was seale::l. The three-way stop-cock was kept closed during the determinations to prevent diffusion. It was not greased and the film of liquid around it afforded ample conductance for the minute cuxrent required to make the measurements. The cells were cemented into a brass holder (h) with glycerine and litharge cement. The whole cell was supported by a brass rod (r) which was bolted Page 9 to the holder. A clamp attached to this and loosely screwed to a rod above the them.ostat :formed a hinge on which the cells could be rocked. All electrical connections were made by means of mercury cups, each electrode having a. separate cup. Figure 2 shows the position of the cell in the thermostat, the saturators and the hydrogen genera tor. The motor in the right fore- ground is the thermostat stirrer. It was f9und that when this was running 1t r&.2 affected the potentiometer, so while readings were being taken the current was turned of'f. Figure 3 show~ the general ar- rangement o:f the apparatus. The Page 10 motor ()In) which rocked the cell was placed at a distance, so that this could be kept running while measurements were being made. The electrical measurements were made by means of a Leeds and Northrup potentiometer (No.34346), used in conjunction with a galvonometer2 of the D'Arsenval type (No.34459) and a Weston standard cell ( No. 3528 ). This cell agreed with one calibrated 3 by the Bu.ree.u of standards within o. 00005 vol ts. As a considerable quantity of bismuth dissol.ved of'f ·the electrodes during a run_,it was necessary to analyse the solutions at its conclusion. This was done by pi_p etting a definite quantity of solution :from the cell, adding standard hydrochloric acid,and wrl-'1 titrating "Me sodium hydroxide. The precipitated. bismuth oxy-chloride was then :filtered of'f in weighed 0 Gooch crucibles, dried at 110 C and weighed. The acidity found by this titration was too high by twice 1 the number o:f moles o:f the basic salt :formed. Hence I to obtain the true acidity >this quantity was subtraieted :f'rom the acidity found by the titration. 1. Bi(Cl0 ) + HCl -t- P'20 4 3 ~ BiOCl + 3 H Cl o4 • 2. Also made by Leeds & Northrup. 3. Therra0-electrie effecto wer~ corrected for by shortcircuiting the lends at the celJ.;l.\Y placing them in the same mercury CUP:-; This correction was found to be entirely negligible. Page . 11. To test this methOd,salr!I)les of bisrm.ith weighing o.0412 grams and o.0428 grams,respectively, were dissolved in nitric acid and the excess of acid evaporated off. An excess of hydrochloric acid was added 1 and then a solution of sodium hydroxide,.until the solution was neutral to methyl orange. The precipitated bismuth oxy-chloride weighed 0.0514 and o.0532 grams, respectively, which is the equivalent of o.0412 and o.0426 grams of the metal. This showed that the precipitation of bismuth in this manner w-e.s sufficiently accurate for the purpose. Precipitation as a sulphide, carbonate and electrical precipitation as a metal 1.rrere tried. The first two methods were less convenient and the ) latter was less accurate. Proc~ure~ The hydrogen side of the cell was washed thoroughly four times with perchloric acid of the strength used in the determination I and then filled until the solution almost covered the electrodes. Next 1 pres- sure was applied by blovring on the hydrogen outlet tube, thus forcing the liquid up the siphon tube. when the arm of the siphon was completely filled, the three-way stop-cock wa..s quickly turned, shutting off the hydrogen cell completely. Page 12 The bismuth cell was then rinsed four times and filled, The solution was drawn up into the siphon and through the three-way stop-cock and the upper stop-cock was closed, Hydrogen was th.en run into the cell for at lea.st three hours to saturate the perchloric acid and displaced the air in the cell, The bismuth electrodes were inserted and the joints sealed with paraffin. The cell with the pre-saturator attached to it was placed in the thermostat and rocked. In about an hour the electromotive force of the cell was steady. This slowly increased as the bismuth dissolved off the electrode and consequently the concentration of the bismuth-ion around the electrode increased. 'rhe rate of dissolving depended on the concentration of the bismuth. perchlorate already present. The rate of increase of the electromotive fdrce never exceeded 0.001 volts per hour. When a steady rate of increase was reached., readings 1.11Tere taken and the bismuth electrodes removed i1nmediately to prevent more bismuth from dissolving. The bismuth perchlorate solution was t.hen taken from the cell and analysed for bismuth perchlorate and perchloric acid,in the manner described above. For several runs the solution in the hydrogen cell was also analysed., but since no appreciable change Page 13 was detected in the concentration of the perchloric acid, this practice was discontinued. The cell measured may be represented as follows: (C for,mal) + HCl04(C 1 formal), HCl04 (C I t formal), tr 2 The measured electromotive force is the algebraic sum of the potential set up by the bismuth electrode and the solution of tts ions, of that due to the liquid junction>and of that at the hydrogen electrode. The hydrogen electrode was corrected to the normal hydrogen electrode in the usual manner, taking into account the pressure of the water vapor above the solution and the barometric pressure. since the concentration of the per·chloric acid is large compared with that of the bismuth perchlorate, the liquid junction is practically that due to the two acid solutions. The liquid potential is then given by the formula: A -I\ .:. 0104 /\-H-._,.-+-/\ __C_l_O~- = / 'H + Ln The liquid :potentials tb.us calculated were always less then 0.01 volt and were probably correct to two mi~ivolts. Page 14 The specific electrode potential was then calculated :from a bismuth electrode :potential refeITed to the normal hydrogen electrode. No data could be found concerning the ionization of bismuth salts so the ionization of bismuth perchlorate was assumed to be the same as that of lanthanum nitrate (La(N0 ) ). l 3 3 In allowing for the exces s of parchlora te ion from the perchloric acid, theru.le that the ionization of a mixture of.' salts depends only on the concentration of the common ion, was employed. The ionization was therefore assumed to be that of lanthanum nitrate at a concentration equal to the sum of the concentrations of bismuth perchlorate and perchloric acid. The ionization of the perchloric acid in the hydrogen cell was calcu2 lated f'rom Ostwald's conductance data for that acid. The complete calculation may be expressed tb.us: E.M.F • .,.(;Bi)- ( }i Ln ~1"') - ( ~ H+~/lc10~ Ln V\ H+ 110104 g~) -,.{B......'E. Ln %.L.(R....7. L_n li.Q.) F J' 2F Pti 2 H 1. Noyes and Jrohnson, J. Am. Chem. So.c. 31, P. 987, 1909 2. Le.ndolt, Bornstein & Roth, Tabellen, 4 Auf'lage, Seite 1112 (1912). Page 15 The details of the five determinations, and the specific E.M.Flscalculated from each are given in Table I. TRBLE I Hydrogen Cell Bismuth Cell Molsfr..itre Bf++- HCl04 H..,. H010 4 n-+ • 00286 . 060 .057 • 079 • 0745 • 0157 • 0097 .120 .112 • 079 • 0745 . 0151 • 0093!: .121 .113 .0795 • 0746 Run Elerftides Bi( 0104 }~ l Bi(N03)3 .0042 2 do. 3 Bi(Cl04)3 ' do. 4 and Bi{N0 3 ) 3 .0014 • 0009 • 0795 • 0746 . 079 • 0745 5 Bi(N03)3 • 0014 i • 0010 .0795 . 0746 • 079 • 0745 Liquid H2Pressure spe~~t.lec correction Pote.ntial Meas.E.M.F. PotentiaJ Run Barometer 1 745 - . 3120 + .0046 -.0006 -.291 2 745 - .3166 ,e .0070 -.0006 -.297 3 745 - .3149 - • 0071 - • 0006 -.296 4 745 - .3121 0 -.0006 -.306 5 745 - .3088 0 -.0006 -.302 Mean Value Page 16 -.298 volts. The second method of determining the specific el ectroo'tpotential of bismuth was based on the principle that when a solution containing the . :tons of two metals is in contact with these two me.tals, equilibrium is established when the ion concentrations are such that the electromotive forces set up by these metals and the solution of their ions are de equal. Those metals whose specit"ic electrq, potentials have almost the same value will therefore come to such e.n equilibrium that ions of both metals are p3:esent in determinable amounts. Method A glass stoppered bottle containing a slightly acid solution of cu~ric perchlorate, solid bismuth oxide, cupric oxide, metallic bismuth and metallic copper, was sealed with paraffin, placed in the thermostat and. rocked for four days at a temperature 0 1 of 25 c. 1. The copper perchlorate was made by heating Kahlbaum• s cupric oxide with dilute perchloric acid. For the metal Kahlbaum•s reduced powdered. copper was used. Bismuth and bismuth oxide were prepared in the same manner as for the electromotiv e force determination. Page 17 At the end of this time it was found that all the metallic bismuth had dissolved and tb.at a considerable quantity of a white amorphfl.s powder (prob" ably bismuth basic :perchlorate) had precipitated. The solution was then filtered, a little dilute perchloric acid added, and put back into the thermostat with a new supply of finely divided metallic bismuth and cop-per. When it had been rocl<.ed for three days more in the thermostat, the solution was removed, filtered and analyzed for bismuth and copper. Analyses The bismuth was precipitated as the oxy-chloride in the manner described above (Page 11 ). The pre- ctpi tate was then filtered o:f:f in weighed Gooch cruo cibles, dried at 110 c. and weighed. The filtrate then contained about two milligrams of copper per 100 cubic centimeters of solution and about the sa.me amount of bismuth.(This loss of bismuth is negligible}. The presence of this bismuth rendered the usu.al methods o:f gravimetric analysis impracticable . .Ammonia was therefore added to the solution, thus forming the .. -f cOmpleX ion Cu(NH3 14 which has a clear blue color. colorimtt11-ic BY.... com};)ar:taon with standard solu.t ions tb.e concentration of the copper could be estimated to within six or eight Page 18 1 per cent. Results The results of two independent runs e.re given in Table 2. The specific electrode potential was calcu- lated by the equation: E CU - R......T. }T F X Ln (concentration cupric-ion)= EBi _ 1L1 x Ln ( concentration Bismuth-ion) NF The speci:f'ic electrode potential of coppe1· 2 ( to cupric-ion solution) was taken as -o. ~5 • The ionization of bismuth perchlorate was assumed to be the same as that of lanthanum nitrate and that of eupric perchlorate to be that of barium chloride. J; 1. Kn err or of 10 per cent in the concentration of copper would make a differenee of 0.002 vol ts, in the final result. The cupr~-ion is negligible since the value of the ratio <&oncentration cu (Concentration cu) 2 ' calculated from the speciflic electrode potentials ?+ + cu, cu ( lM )and QB_, cu (lM) is greater than 100, ooo. 2. G.N.Lewis and w.M.Lacy, J.Am.Chem.soc.36, 804-10, ( 1914) The va111e ~io ..~.35 was obtained. from the cell cu, cu..,.t; / s~-, Hg S04 Page 19 + Hg. TABLE II -+ +-t- Cu++ Run Bi(Cl0)4-J Bi, Cu(Cl0)44- 2 1 .0517 ,0316 .00070 . 00056 .283 2 .0456 .027~ . 009.5.5- .00044 .282 EBi This result agrees fairly well with the value obtained from the electromotive force determination. Note 2, co1ninu.ed from Page 19. For the cell Cu, CuS01: /. 005M.), CuS04-(. 051L), MgS04 ( .05M. ), KCl( .lM. ), Kvl(1¥,.), Hg 2 Cl 2 Hg ·rhe value was found to be -0. 33. 'I'hi s was considered less accurate owing to the uncertainty in calculating the liquid potentials. Page 20